Sansui 9090DB Output Problems

[Plimpington2]

There are lots of well know and documented errors in service manuals. This may be/probably is one of them? I don't have much under the hood time with the DB versions of these.

A lot of straight 8080's and 9090's which are a little different.

I will have to keep an eye out for this. So far, the 9090 manual and board printing seem ok. But I have a 9090db waiting as well.

 

[CaseyWKC]

Lets do a reset.

Put the black wire from the protection board back.

Remove the driver board and check the voltages at the fuses.

If they are near zero (low or no mVDC) the protection circuit should blink the lights and close the relay.

Okay, all points resoldered back to the protection board.

F02 measures 88mv across

F01 I see 55 volts.

still on dbt - will not come out of protect

I also note that TR03 and TR04 voltages are crazy, jumping around sporadically until my meter reads overload over and over again.

 

[mrk229]

Okay, all points resoldered back to the protection board.

F02 measures 88mv across

F01 I see 55 volts.

still on dbt - will not come out of protect

I also note that TR03 and TR04 voltages are crazy, jumping around sporadically until my meter reads overload over and over again.

At the fuses we are measuring offset voltage. That is measured from one end of the fuse to ground. We are assuming the fuse is good .
Did you really measure across the fuse?

And since you mentioned TR03 and TR04 that tells me you did not remove the driver board first.
That said what specifically what voltages are jumping around, E, B, C?

By having the driver board out I am hoping to confirm the output transistors are OK and with the inputs to the protection circuit protection being zero volts that the protection circuit pulls the relay in.

If that takes place the problem area becomes the driver board and maybe it's power supplies.

 

[CaseyWKC]

At the fuses we are measuring offset voltage. That is measured from one end of the fuse to ground. We are assuming the fuse is good .
Did you really measure across the fuse?

And since you mentioned TR03 and TR04 that tells me you did not remove the driver board first.
That said what specifically what voltages are jumping around, E, B, C?

By having the driver board out I am hoping to confirm the output transistors are OK and with the inputs to the protection circuit protection being zero volts that the protection circuit pulls the relay in.

If that takes place the problem area becomes the driver board and maybe it's power supplies.

I am taking measurements at the fuses from one end to ground, yes.

TR03 and 04 I was referencing was in the protection circuit. I traced it back to the power supply board and I found TR02 on the power supply board is shorted (reading as two diodes).

I am now looking for a good replacement for 2sb560 - I have a KSA1220 ?

I have not had the driver board in for any of this.

 

[Plimpington2]

Okay, all points resoldered back to the protection board.

F02 measures 88mv across

F01 I see 55 volts.

still on dbt - will not come out of protect

I also note that TR03 and TR04 voltages are crazy, jumping around sporadically until my meter reads overload over and over again.

Oh, hold on now. You can’t expect it to come out of protect on the dim bulb. Mine does not come out of protect on the dim bulb. If you’ve removed the driver board, there is no reason this thing should not come out of protect. Do you have a variac? Remove the driver board and bring it up slowly, sucking voltages at the PSU. The unit should come out of protect around 60
Volts on the incoming line.

 

[CaseyWKC]

Oh, hold on now. You can’t expect it to come out of protect on the dim bulb. Mine does not come out of protect on the dim bulb. If you’ve removed the driver board, there is no reason this thing should not come out of protect. Do you have a variac? Remove the driver board and bring it up slowly, sucking voltages at the PSU. The unit should come out of protect around 60
Volts on the incoming line.

I have had this unit come out of protect with the driver board installed along with the outputs a number of times now. I have a 150w bulb in my dbt, my crown psa2's even sprang to life on them most of the time

I replaced the shorted 2sb560 to no change, I'm guessing it was fine, just a misreading on my part due to the corrosion on the legs.

So at the inputs 03 and 04 coming into the protection circuit across those fuses I still am getting that 88mv and then the 55 volts

The protection light is no longer flashing red either, it is just a SOLID red.

 

[mrk229]

I have had this unit come out of protect with the driver board installed along with the outputs a number of times now. I have a 150w bulb in my dbt, my crown psa2's even sprang to life on them most of the time

I replaced the shorted 2sb560 to no change, I'm guessing it was fine, just a misreading on my part due to the corrosion on the legs.

So at the inputs 03 and 04 coming into the protection circuit across those fuses I still am getting that 88mv and then the 55 volts

The protection light is no longer flashing red either, it is just a SOLID red.

I agree with a 150 watt bulb the voltage drop should be very low under idle conditions. However there is not a lot of voltage headroom in the relay driver circuit.

If you want pop the fuses out of the protection board and see if the relay closes with the DBT.

You should not have 55 volts at what I think you are calling pin 4 with the driver board out. 88mV is suspicious but not totally alarming.

You need to find the source of that 55 volts. Check the NPN output transistors on the channel with 55 volts.

 

[CaseyWKC]

I agree with a 150 watt bulb the voltage drop should be very low under idle conditions. However there is not a lot of voltage headroom in the relay driver circuit.

If you want pop the fuses out of the protection board and see if the relay closes with the DBT.

You should not have 55 volts at what I think you are calling pin 4 with the driver board out. 88mV is suspicious but not totally alarming.

You need to find the source of that 55 volts. Check the NPN output transistors on the channel with 55 volts.

Pulled the outputs on the affected channel, reinstalled the fuses, powered it on and relay pulled in, no more 55v or 88mv, 0v across the fuses on protection board.

All of these outputs test fine in my tester and with a standard diode drop test. And I was using them before with no issue. That stinks.

 

[mrk229]

Pulled the outputs on the affected channel, reinstalled the fuses, powered it on and relay pulled in, no more 55v or 88mv, 0v across the fuses on protection board.

All of these outputs test fine in my tester and with a standard diode drop test. And I was using them before with no issue. That stinks.

OK some good data points. It appears the protection circuit is working.

My guess is the transistors are OK. They are real ones from a legit vendor, yes?

Go over all of the wiring going to the output transistor sockets for the bad channel, look for solder bridges at the wire connection points.

Have a good look at the sockets, do the transistor pins fit snugly in them, nothing bent and touching other connections etc. Basically a very thorough close visual inspection.

 

[CaseyWKC]

OK some good data points. It appears the protection circuit is working.

My guess is the transistors are OK. They are real ones from a legit vendor, yes?

Go over all of the wiring going to the output transistor sockets for the bad channel, look for solder bridges at the wire connection points.

Have a good look at the sockets, do the transistor pins fit snugly in them, nothing bent and touching other connections etc. Basically a very thorough close visual inspection.

Phew.

Swapped channels to confirm it was wiring or outputs, relay pulls in with all outputs installed. Yay!

Remounting protection board and will update this when I see what's going on after reinstalling the driver board.

And yes the four trans in the problematic channels are the originals, the other channel I replaced with MJ21194 and MJ21193's.

 

[mrk229]

Phew.

Swapped channels to confirm it was wiring or outputs, relay pulls in with all outputs installed. Yay!

Remounting protection board and will update this when I see what's going on after reinstalling the driver board.

And yes the four trans in the problematic channels are the originals, the other channel I replaced with MJ21194 and MJ21193's.

You seem to have a knack for the oddball issues.

Since that driver board has been IN-n-OUT so many times take a close look at the solder joints for the pins on the PS board.

 

[CaseyWKC]

You seem to have a knack for the oddball issues.

Since that driver board has been IN-n-OUT so many times take a close look at the solder joints for the pins on the PS board.

Hoorah, sound through both channels, offset is at 0.

Onto bias, I always have trouble with bias @ fuseholders using mah, I need a better meter.

Is there anyway to cheat to adjust in mv or get it close across anything?

Currently when trying to measure bias at the fuseholders I get sporadic readings. The pots don't seem to have any effect.

Update : god this sm has so many errors, did not know the fuse holders for L and R channel were even labeled wrong! Wow!

 

[mrk229]

Good news bad news. Good, yes there is a way to cheat. Bad, I can't find the mV values.

Anyhow you will have to try it the hard way first, and then measure the needed value and set the other channel using that value.

I almost always start with my meter in the high amp setting, mine is 10 amps. Less chance of blowing a meter fuse if something is wrong.
In high range mA of course will be after the decimal point. 0.030 Amps is 30mA

Once in the ballpark you can reconfigure the meter for mA range and dial it in.

Here is where you can help me since I can't find the mV values right now. Get one channel dialed in and then using my next post we can measure the values and apply it to the other channel.

 

[Plimpington2]

Pulled the outputs on the affected channel, reinstalled the fuses, powered it on and relay pulled in, no more 55v or 88mv, 0v across the fuses on protection board.

All of these outputs test fine in my tester and with a standard diode drop test. And I was using them before with no issue. That stinks.

I keep getting confused by your language. When you say you tested voltage "across the fuses" (or across anything), are you really checking voltages across the fuses? An intact fuse would always show 0 volts if you check across it (no matter what the voltage is on one side of the other). Or do you mean you are checking voltages "at" the fuse (either one side of the side) with one lead grounded to chassis, ground, etc. I just want to make sure I understand what you are doing.

 

[CaseyWKC]

I keep getting confused by your language. When you say you tested voltage "across the fuses" (or across anything), are you really checking voltages across the fuses? An intact fuse would always show 0 volts if you check across it (no matter what the voltage is on one side of the other). Or do you mean you are checking voltages "at" the fuse (either one side of the side) with one lead grounded to chassis, ground, etc. I just want to make sure I understand what you are doing.

My apologies, that is my fault, I was not measuring across the fuses I was measuring at the fuses. I will do better at being more clear going forward and using the correct terminologies. I understand that sometimes by making mistakes like that I just make things more confusing.

Regardless, I'm dialing in the 30mah of bias now that I realized the SM had the L and R channel fuses swapped.

I have 25-30mah on both channels. About to start testing after reinstalling the heatsink.

Now i Get to focus on the dolby board again, no r channel in dolby fm

 

[mrk229]

My apologies, that is my fault, I was not measuring across the fuses I was measuring at the fuses. I will do better at being more clear going forward and using the correct terminologies. I understand that sometimes by making mistakes like that I just make things more confusing.

Regardless, I'm dialing in the 30mah of bias now that I realized the SM had the L and R channel fuses swapped.

I have 25-30mah on both channels. About to start testing after reinstalling the heatsink.

That is awesome, however I am not sure what ended up being the problem/solution we were chasing?

And it seems like it was OK once or twice and something else popped up. I really lose sleep over not knowing exactly what caused the problem.

 

[CaseyWKC]

That is awesome, however I am not sure what ended up being the problem/solution we were chasing?

And it seems like it was OK once or twice and something else popped up. I really lose sleep over not knowing exactly what caused the problem.

Haha yes it bothers me too, but I have learned to sometimes not ask too many questions, especially when the project has been on the bench on and off for a month or two.

Everything is working how it should except for rec 2 on the dolby board, no r channel audio and I get a nasty pop when I switch to it with the volume up any. Rec 1 works fine.

Gonna go over the dolby board again but I'm honestly kind of afraid to pull it with all of the trace repair that's been done.